Slow leak, 4/32, right rear tire

I had a slow leak develop in my right rear tire over the past month. I'd rotated the front and back last month with the front wear at 6/32 and rear at 4/32 ... I was slow to rotate them last fall. But Firestone says the leak is in the non-repairable part. So the question is what to do:

• Stop-leak/self repair
• Buy a pair and replace full-size spare

Stop-leak/self repair

I have access to a shop with tire repair equipment. I could get an inside patch; locate the leak; and fix it myself. At the rate the front tires wore, I should get another two years out of these tires, ~70-80k miles.

Given it is a slow leak, I could try the latex inflation systems. Lower the air pressure and use one of the quick fix tire systems and inflate the tire to normal 32 psi and do some high speed driving to 'seal' the leak. Come back and inflate the tire to proper pressure. The problem is the sticky latex might gum up my tire pressure gauge.

We used this on our minivan when I discovered the spare had a slow leak and no pressure at 3:00 AM Monday morning. I'd pulled into a quick-market and having nothing to lose, used a can on the spare. We got home and I repaired the tire the next week. No long term use of the latex, quick-fix system. Anyone have experience to share?

Replace Pair

Since June 2008, I've been conducting an experiment with oversized, Sumitomos:

	Column 1	Column 2	Column 3	Column 4	Column 5
0	size	rev/min	comment
1	175/65R14	919	Original size but indicated speed was 1% high.
2	175/70R14	886	Slight steering stability improvement	3% low.
3	185/70R14	867	Wider	more drag	5% low.
4	195/70R14	849	Widest and 7% low.

Sumitomo T4s

Even though I've been adjusting for the larger diameter tire in the mileage records, there is no evidence of improved efficiency. Drag is drag and regardless of the tire rotation speed, we must pay the piper.

The lower indicated speed can lead the driver to faster true speeds and higher drag. I'm the only driver of the 03 Prius so I typically calculate the difference and adjust. But that happens when I remember to adjust. In fact, I suspect I may have forgotten the times when I might have failed to adjust. I really need some way to get a calibrated speed ... perhaps a GPS unit. Perhaps it is time for a full vehicle data recording system. . . . a fun project.

I do like the improved steering stability of the oversized tires. If by going larger I can achieve even greater stability ... this would be a good thing.

Conflicted

Being frugal, I like fixing the failed tire and getting another couple of years of service out of the set. I've gotten ~30k miles of service out of this set so reaching closer to ~70-80k miles is appealing. Repair cost is nominal, sweat equity, and defer tire experiments another year.

I'm not too thrilled with the latex solution except to extent tire life while a total data recording system is set up. This would let me accurately document before and after performance ... in fact all critical vehicle performance.

I also like the idea of testing the extreme edge of NHW11 tires, the 195/70R14. Putting them on the rear for another year and replacing the worn-out, full-size spare makes sense. Then I can swap them with the front to evaluate: steering stability and fuel efficiency effects.

Thoughts?

Bob Wilson

 

Hey folks, calm down. The leak is so slow I can simply top off the tire when the pressure sensor cap shows a problem. I haven't seen the leak but will before moving forward. What bothers me is how it seemed to happen so soon after having the tires rotated. I didn't have that problem when I last rotated my own tires . . .

I still have a full size spare from the last tire change and the leaky tire is now an unpowered, trailing, rear tire. This is the commuting car as we use the 2010 for family trips. Still, I appreciate your economic analysis:

• $50-56 - per tire cost, not counting shipping and mounting
• $20 - mount the tires

The area I'm interested in is moving the 42 mph hybrid threshold higher. The larger diameter tire will move the 42 mph threshold up to 45 mph. Now this may not seem like much but it means a little faster in hybrid mode. But I need to accurately know the vehicle speed without the mental exercise. The good news is I can swap the front and rear tires to change the drive diameter and move the hybrid speed.

My plan is to use a Garmin GPS for the speedometer. Then use a Graham scanner or equivalent to capture engineering data. This will let us quantify the effects of tire diameter change.

Bob Wilson

 

It is relative to the other three tires and may be closer to 5 psi per month. I haven't quantified it yet. I took to Firestone in the hope it was a regular puncture. Their diagnosis was a surprise and I'll use the soapy water test in the morning.

Bob Wilson

 

It is too early to tell but with the pressure caps, it is easy enough to monitor. My only regret is not titling the thread "Very slow leak." The irony is a monthly pressure loss of 1-1.5 psi per month is also a slow but nearly universal 'leak.'

Bob Wilson

 

The last tire top-off was 4/27 and today, I noticed the pressure cap is showing low. These are 50 psi pressure caps so I'm probably around 38-40 psi . . . and it is about time to top off the gas tank. Also, I now have a Garmin 265WT mounted, which provides bluetooth and GPS speedometer and trip meter.

I'll top off the tank tonight and reset the Garmin trip record. Next week I'll order a pair of oversize tires from Tire Rack and do the switch and alignment check. I'll probably swap the casing for my spare since the low wear of the 'good tire' will make a better spare.

For those interested in the Sumitomo T4 tire specifications:

• 175/65R14 - Toyota's replacement tire, 1019 lbs max weight, 919 revs/mile, 5-6" rim width
• 175/70R14 - Current tires soon to be rear, 1102 lbs max weight, 886 revs/mile (~3% speedometer error) 4.5-6" rim width
• 195/74R14 - Next pair, 1321 lbs max weight, 849 revs/mile (~7% speedometer error,) 5-6.5" rim width

Without the GPS speedometer, this would be an impractical experiment.

Thoughts?

One early test will be a high-speed drive over a speed bump. There had been one report of some wider tires, Yokohamas(?) not clearing the wheel wells on bumps. If this is the case, I want to find out early. I'll probably put them on the rear since I don't want to compromise steering in this test. Once I know they clear the rear wheel wells, I'll run them for a tank to get an idea of the baseline MPG. I'll then swap them to the front and again, run a tank and some benchmarks.

Bob Wilson